How can I edit or add to a particular field without pull the all object

Question

1. How I can do just this ( a.myFavorits.Add()) without pulling the all object to var a , because a has a lot of data, and I don\'t

Answer 1

I'm guessing this is what you want? I don't see you 'editting' I only see you adding.

using (var db = dataBase())
{
    var a = new user(); 
     .... 
     //set properties etc..
     ...
    a.myFavorits.Add(new BE.FavoritsUsersLong { myLong = f });
    db.users.Add(a);
    db.SaveChanges(); 
}